The present invention generally relates to lace for footwear, and more particularly to a method for constructing a core/sheath lace having enhanced knot retention.
The major purpose for lace used in footwear is to adjust the size of the shoe to snugly fit the foot, and also to allow rapid shoeing and unshoeing of the foot. Most commonly, a bowknot is used to prevent the lace from loosening. The frictional characteristics of the lace surface play an important role in the functionality of the lace. With high lace to eyelet friction, it will be more difficult to initially lace the shoe, and more difficult to loosen the laces when removing the shoe. With low lace-to-lace friction, on the other hand, a bowknot may repeatedly become untied through the course of a day. This can be more than simply annoying if, for instance, one is carrying a heavy load, or running a marathon. Many mechanical devices and special shoelaces have been devised to solve this problem. These approaches suffer from a number of deficiencies, but a deficiency common to all is that the aesthetic of the shoe is altered, usually in a negative direction. As the lace is one of the most visible portions of the shoe, replacing it with another lace designed for functionality will have limited appeal, and replacing or accessorizing the lace with a mechanical locking device will appeal only to the desperate. Such laces and mechanical locks are taught in U.S. Pat. No. 6,212,743 to Cohen, U.S. Pat. No. 5,272,796 to Nichols, U.S. Pat. No. 4,780,936 to Brecher, and U.S. Pat. No. 5,673,546 to Abraham et al. None of these lace systems have addressed the concurrent problems of assuring that the laces easily slide through the eyelets or holes provided for them, resisting knot loosening, and maintaining the aesthetics of the lace or footwear/lace combination.
The present invention provides a method for altering the self-frictional characteristics under compression of at least one free lace end of an article of footwear, so that a bowknot subsequently tied has greater resistance to loosening. As a preferred embodiment, the knot is tied first and a fluid comprising a frictive agent is applied at least to the tied knot and allowed to dry. The present invention also provides a frictive fluid composition that comprises a frictive powder. The frictive powder preferably is colorless and has low relative opacity, preferable less than 10, more preferably less than 5, and most preferably less than 1, so as to allow its use with minimum appearance change of the lace, especially colored or black lace. The frictive fluid preferably has a viscosity of less than 1000 cP, and more preferably less than 100 cP, and most preferably less than 50 cP, so as to allow the penetration of the frictive fluid into the lace, and to avoid build up on and resultant discoloration of the lace surface. A preferred frictive powder comprises silica, especially amorphous silica. The frictive powder must produce a breakaway force ratio (BFR), defined below, that is greater than one, more preferably at least 1.25, and most preferably at least 1.5. It is preferred for that the characteristic primary particle size is less than 100 nm, and preferably less than 50 nm.
In another embodiment, a shoelace having a porous sheath is constructed around a lace core having a reservoir of powder. Mechanical action such as tying and untying of the lace frees powder (preferably silica) from the core that then migrates to the outer surface of the sheath where the powder enhances the knot holding power of the lace.
It is an object of the present invention, therefore, to provide a method of lace treatment for increasing the breakaway force ratio (BFR) of a shoelace knot.
It is another object of at least one embodiment of the invention to provide a method for application of a frictive fluid to a lace of an article of footwear.
It is another object of at least one embodiment of the invention to provide a frictive fluid composition that does not substantially change the appearance of a shoelace.
It is another object of at least one embodiment of the invention to provide a core/sheath lace for footwear wherein the core comprises a reservoir of frictive powder.